Measuring and visualizing particle deposition onto substrates is very important for a variety of industries. Medical techniques have been developed to assess foreign particle deposition on lung tissues, and to evaluate risks of blockages to blood vessels. Methods have been developed for determining deposition rates of charged particles onto substrates for the purpose of measuring electrostatic attraction. Computer simulations have also been used in order to observe particle deposition as a means of measuring air filter efficiency. These techniques generally provide quantitative data to describe their results. Interpreting this data typically requires either specialized training in the relevant field, or some secondary processing to communicate trends and effects. Therefore, these techniques do not provide an efficient means for communicating benefits or detriments based on particle deposition onto substrates. Also, none of these techniques provide an environment where particle deposition may be observed as various additives are introduced into a system.
Flow cell units are known (see U.S. Pat. No. 4,974,952), and are often used to introduce various drugs and additives into a fluid environment to analyze their effects. Generally, flow cell units are applied to an array of biological research applications. Flow cells are commonly used in flow cytometer configurations. Such devices may be used to analyze several thousand particles per second, and can actively separate and isolate particles having specified properties. Flow cytometry is most commonly associated with cellular biological applications such as fluorescence-activated cell sorting. However, the technology has also been broadly applied to medical and bioengineering experimentation as well.
Attempts have been made to use flow cells to visualize particle deposition on substrates. Previous attempts to apply the technology to particle-substrate visualization have used flow cell DIC microscopy to visualize coacervate interaction with hair fibers. J. Cosmet. Sci., 58, 637-650 (November/December 2007). Coacervate phases are important to aid in deposition of conditioning particles to hair fibers, and flow cell DIC microscopy is useful for visualizing deposition efficiency of various personal care compositions on the hair substrate.
However, previous flow cell designs position the hair fiber between two slides, through which a liquid solution is caused to flow. This configuration results in an inefficient system, in that the liquid solution cannot flow around the entire hair fiber because the fiber is “sandwiched” between the two flow cell slides, being in contact with both. Therefore, the liquid solution can only interact with the edges of the substrate which are not in contact with the slides. Accordingly, during analysis, only the edges of the visible substrate are exposed to the liquid solution, and visualization suffers. Furthermore, “sandwiching” often causes additives to deposit onto the surface of the slides, as there is insufficient spacing to allow for some particles to pass through the system. Therefore, deposition onto the substrate becomes indistinguishable from other intervening additives.
Based on the foregoing, there is a need for a flow cell apparatus which provides a means for visual analysis of particle-substrate interaction, whereby a greater surface area of the substrate is exposed for analysis.